Graphene oxide based multilayer capsules with unique permeability properties: facile encapsulation of multiple drugs

Novel composite graphene oxide (GO)/poly(allylamine hydrochloride) (PAH) multilayer capsules have been fabricated by layer-by-layer (LbL) assembly. They were found to possess unique permeability properties compared to traditional LbL capsules. These hybrid capsules showed special ``core-shell'' loading property for encapsulation of dual drugs simultaneously into the core and shell of the capsules respectively.

Near-infrared light-responsive graphene oxide composite multilayer capsules: a novel route for remote controlled drug delivery

A novel and simple route for near-infrared (NIR)-light controlled release of drugs has been demonstrated using graphene oxide (GO) composite microcapsules based on the unique optical properties of GO. Upon NIR-laser irradiation, the microcapsules were ruptured in a point-wise fashion due to local heating which in turn triggers the light-controlled release of the encapsulated anticancer drug doxorubicin (Dox) from these capsules.

Composite cyclodextrin-calcium carbonate porous microparticles and modified multilayer capsules: novel carriers for encapsulation of hydrophobic drugs

Novel composite cyclodextrin (CD)-CaCO3 spherical porous microparticles have been synthesized through Ca2+-CD complex formation, which influences the crystal growth of CaCO3. The CDs are entrapped and distributed uniformly in the matrix of CaCO3 microparticles during crystallization. The hydrophobic fluorescent molecules coumarin and Nile red (NR) are efficiently encapsulated into these composite CD-CaCO3 porous particles through supramolecular inclusion complexation between entrapped CDs and hydrophobic molecules. Thermogravimetric (TGA) and infrared spectroscopy (IR) analysis of composite CD-CaCO3 particles reveals the presence of large CDs and their strong interaction with calcium carbonate nanoparticles. The resulting composite CD-CaCO3 microparticles are utilized as sacrificial templates for preparation of CD-modified layer-by-layer (LbL) capsules. After dissolution of the carbonate core, CDs are retained in the interior of the capsules in a network fashion and assist in the encapsulation of hydrophobic molecules. The efficient encapsulation of the hydrophobic fluorescent dye, coumarin, was successfully demonstrated using CD-modified capsules. In vitro release of the encapsulated coumarin from the CD-CaCO3 and CD-modified capsules has been demonstrated.

Stimuli-responsive weak polyelectrolyte multilayer films: A thin film platform for self triggered multi-drug delivery

Polyelectrolyte multilayer (PEM) thin film composed of weak polyelectrolytes was designed by layer-by-layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) for multi-drug delivery applications. Environmental stimuli such as pH and ionic strength showed significant influence in changing the film morphology from pore-free smooth structure to porous structure and favored triggered release of loaded molecules. The film was successfully loaded with bovine serum albumin (BSA) and ciprofloxacin hydrochloride (CH) by modulating the porous polymeric network of the film. Release studies showed that the amount of release could be easily controlled by changing the environmental conditions such as pH and ionic strength. Sustained release of loaded molecules was observed up to 8 h. The fabricated films were found to be biocompatible with epithelial cells during in-vitro cell culture studies. PEM film reported here not only has the potential to be used as self-responding thin film platform for transdermal drug delivery, but also has the potential for further development in antimicrobial or anti-inflammatory coatings on implants and drug-releasing coatings for stents. (C) 2015 Elsevier B.V. All rights reserved.

Encapsulation and release of rifampicin using poly(vinyl pyrrolidone)-poly (methacrylic acid) polyelectrolyte capsules

Poly(vinyl pyrrolidone) and poly(methacrylic acid) multilayer capsules based on hydrogen bonding have been prepared by the layer-by-layer approach and used to encapsulate and release rifampicin, an antituberculosis drug. Removal of silica core using a buffer of ammonium fluoride and hydrofluoric acid at about pH 3 was found to produce better capsules than hydrofluoric acid alone. An eight-layered capsule had a wall thickness of 20 rim. Maximum encapsulation was found to be about 86 mu g at 40 degrees C with 1 +/- 0.2 x 10(6) capsules. Release studies showed a burst kind of release and maximum release was obtained above pH 7 where the capsules disintegrate rapidly thereby releasing the drug in a short period. Interactions studies with Mycobacterium smegmatis showed that the capsules were cytocompatible and the released drug functioned with the same efficacy as the free drug.

Polyelectrolyte/silver nanocomposite multilayer films as multifunctional thin film platforms for remote activated protein and drug delivery

We demonstrate a nanoparticle loading protocol to develop a transparent, multifunctional polyelectrolyte multilayer film for externally activated drug and protein delivery. The composite film was designed by alternate adsorption of poly(allylamine hydrochloride) (PAH) and dextran sulfate (DS) on a glass substrate followed by nanoparticle synthesis through a polyol reduction method. The films showed a uniform distribution of spherical silver nanoparticles with an average diameter of 50 +/- 20 nm, which increased to 80 +/- 20 nm when the AgNO3 concentration was increased from 25 to 50 mM. The porous and supramolecular structure of the polyelectrolyte multilayer film was used to immobilize ciprofloxacin hydrochloride (CH) and bovine serum albumin (BSA) within the polymeric network of the film. When exposed to external triggers such as ultrasonication and laser light the loaded films were ruptured and released the loaded BSA and CH. The release of CH is faster than that of BSA due to a higher diffusion rate. Circular dichroism measurements confirmed that there was no significant change in the conformation of released BSA in comparison with native BSA. The fabricated films showed significant antibacterial activity against the bacterial pathogen Staphylococcus aureus. Applications envisioned for such drug-loaded films include drug and vaccine delivery through the transdermal route, antimicrobial or anti-inflammatory coatings on implants and drug-releasing coatings for stents. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Enhancing fluorescence signals from aluminium thin films and foils using polyelectrolyte multilayers

In this paper we investigate the application of polyelectrolyte multilayer (PEM) coated metal slides in enhancing fluorescence signal. We observed around eight-fold enhancement in fluorescence for protein incubated on PEM coated on aluminium mirror surface with respect to that of functionalized bare glass slides. The fluorescence intensities were also compared with commercially available FAST (R) slides (Whatman) offering 3D immobilization of proteins and the results were found to be comparable. We also showed that PEM coated on low-cost and commonly available aluminium foils also results in comparable fluorescence enhancement as sputtered aluminium mirrors. Immunoassay was also performed, using model proteins, on aluminium mirror as well as on aluminium foil based devices to confirm the activity of proteins. This work demonstrated the potential of PEMs in the large-scale, roll-to-roll manufacturing of fluorescence enhancements substrates for developing disposable, low-cost devices for fluorescence based diagnostic methods.

Reversible and irreversible pH induced conformational changes in self-assembled weak polyelectrolyte multilayers probed using etched fiber Bragg grating sensors

Polyelectrolytes are charged polymer species which electrostatically adsorb onto surfaces in a layer by layer fashion leading to the sequential assembly of multilayer structures. It is known that the morphology of weak polyelectrolyte structures is strongly influenced by environmental variables such as pH. We created a weak polyelectrolyte multilayer structure (similar to 100 nm thick) of cationic polymer poly-allylamine hydrochloride (PAH) and an anionic polymer poly-acrylic acid (PAA) on an etched clad fiber Bragg grating (EFBG) to study the pH induced conformational transitions in the polymer multilayers brought about by the variation in charge density of weak polyelectrolyte groups as a function of pH. The conformational changes of the polyelectrolyte multilayer structure lead to changes in optical density of the adsorbed film which reflects in the shift of the Bragg wavelength from the EFBG. Using the EFBG system we were able to probe reversible and irreversible pH induced transitions in the PAH/PAA weak polyelectrolyte system. (C) 2014 Elsevier B.V. All rights reserved.

Reversible polyelectrolyte capsules as carriers for protein delivery

A reversible drug delivery system based on spontaneous deposition of a model protein into preformed microcapsules has been demonstrated for protein delivery applications. Layer-by-Layer assembly of poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) onto polystyrene sulfonate (PSS) doped CaCO3 particles, followed by core removal yielded intact hollow microcapsules having a unique property to induce spontaneous deposition of bovine serum albumin (BSA) at pH below its isoelectric point of 4.8, where it was positively charged. These capsules showed reversible pH dependent open and closed states to fluorescence labeled dextran (FITC-Dextran) and BSA (FITC-BSA). The loading capacity of BSA increased from 9.1 x 10(7) to 2.03 x 10(8) molecules per capsule with decrease in pH from 4.5 to 3.The loading of BSA-FITC was observed by confocal laser scanning microscopy (CLSM), which showed homogeneous distribution of protein inside the capsule. Efficient loading of BSA was further confirmed by atomic force microscopy (AFM) and scanning electron microscopy (SEM).The interior capsule concentration was as high as 209 times the feeding concentration when the feeding concentration was increased from 1 to 10 mg/ml. The deposition was initially controlled by spontaneous loading mechanism at lower BSA concentration followed by diffusion controlled loading at higher concentration; which decreased the loading efficiency from 35% to 7%. Circular dichroism (CD) measurements and Fourier transform infrared spectroscopy (FTIR) confirmed that there was no significant change in conformation of released BSA in comparison with native BSA. The release was initially burst in the first 0.5 h and sustained up to 5 h. The hollow capsules were found to be biocompatible with mouse embryonic fibroblast (MEF) cells during in vitro cell culture studies. Thus these pH sensitive polyelectrolyte microcapsules may offer a promising delivery system for water soluble proteins and peptides. (C) 2010 Elsevier B.V. All rights reserved.

A facile route to synthesize silver nanoparticles in polyelectrolyte capsules

We are reporting a novel green approach to incorporate silver nanoparticles (NPs) selectively in the polyelectrolyte capsule shell for remote opening of polyelectrolyte capsules. This approach involves in situ reduction of silver nitrate to silver NPs using PEG as a reducing agent (polyol reduction method). These nanostructured capsules were prepared via layer by layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and dextran sulfate (DS) on silica template followed by the synthesis of silver NPs and subsequently the dissolution of the silica core. The size of silver nanoparticles synthesized was 60 +/- 20 nm which increased to 100 +/- 20 nm when the concentration of AgNO3 increased from 25 mM to 50 mM. The incorporated silver NPs induced rupture and deformation of the capsules under laser irradiation. This method has advantages over other conventional methods involving chemical agents that are associated with cytotoxicity in biological applications such as drug delivery and catalysis. (C) 2011 Elsevier B.V. All rights reserved.

Silver Nanoparticle Synthesis: Novel Route for Laser Triggering of Polyelectrolyte Capsules

We have demonstrated the synthesis of light-sensitive polyelectrolyte capsules (PECs) by utilizing a novel polyol reduction method and investigated its applicability as photosensitive drug delivery vehicle. The nanostructured capsules were prepared via layer by layer (LbL) assembly of poly(allylamine hydrochloride) (PAN) and dextran sulfate (DS) on silica particles followed by in-situ synthesis of silver nanoparticles (NPs). Capsules without silver NPs were permeable to low molecular weight (A(w), 479 g/mol) rhodamine but impermeable to higher molecular weight fluorescence labeled dextran (FITC-dextran). However, capsules synthesized with silver NPs showed porous morphology and were permeable to higher molecular weight (M(w) 70 kDa) FITC-dextran also. These capsules were loaded with FITC-dextran using thermal encapsulation method by exploiting temperature induced shrinking of the capsules. During heat treatment the porous morphology of the capsules transformed into smooth pore free structure which prevents the movement of dextran into bulk during the loading process. When these loaded capsules are exposed to laser pulses, the capsule wall ruptured, resulting in the release of the loaded drug/dye. The rupture of the capsules was dependent on particle size, laser pulse energy and exposure time. The release was linear with time when pulse energy of 400 mu J was used and burst release was observed when pulse energy increased to 600 mu J.

Multilayer assemblies of polyelectrolyte-gold nanoparticles for the electrocatalytic oxidation and detection of arsenic(III)

Multilayers of poly(diallyldimethylammonium chloride) (PDDA) and citrate capped Au nanoparticles (AuNPs) anchored on sodium 3-mercapto-1-propanesulfonate modified gold electrode by electrostatic layer-by-layer assembly (LbL) technique are shown to be an excellent architecture for the direct electrochemical oxidation of As(III) species. The growth of successive layers in the proposed LbL architecture is followed by atomic force microscopy, UV-vis spectroscopy, quartz crystal microbalance with energy dissipation, and electrochemistry. The first bilayer is found to show rather different physico-chemical characteristics as compared to the subsequent bilayers, and this is attributed to the difference in the adsorption environments. The analytical utility of the architecture with five bilayers is exploited for arsenic sensing via the direct electrocatalytic oxidation of As(III), and the detection limit is found to be well below the WHO guidelines of 10 ppb. When the non-redox active PDDA is replaced by the redoxactive Os(2,2'-bipyridine)(2)Cl-poly(4-vinylpyridine) polyelectrolyte (PVPOs) in the LbL assembly, the performance is found to be inferior, demonstrating that the redox activity of the polyelectrolyte is futile as far as the direct electro-oxidation of As(III) is concerned. (C) 2012 Elsevier Inc. All rights reserved.

LbL Fabricated Poly(Styrene Sulfonate)/TiO2 Multilayer Thin Films for Environmental Applications

Fabrication of multilayer ultrathin composite films composed of nanosized titanium dioxide particles (P25, Degussa) and polyelectrolytes (PELs), such as poly(allyl amine hydrochloride) (PAH) and poly(styrene sulfonate sodium salt) (PSS), on glass substrates using the layer-by-layer (LbL) assembly technique and its potentia application for the photodegradation of rhodamine B under ultraviolet (UV) irradiation has been reported. The polyelectrolytes and TiO2 were deposited on glass substrates at pH 2.5 and the growth of the multilayers was studied using UV/vis speccrophotometer. Thicknes measurements of the films showed a linear increase in film thickness with increase in number of bilayers. The surface microstructure of the thin films was characterized by field emission scanning electron microscope. The ability of the catalysts immobilized by this technique was compared with TiO2 films prepared by drop casting and spin coating methods. Comparison has been made in terms of film stability and photodegradation of rhodamine B. Process variables such as the effect of surface area of the multilayers, umber of bilayers, and initial dye concentration on photodegradation of rhodamine B were studied. Degradation efficiency increased with increase in number of catalysts (total surface area) and bilayers. Kinetics analysis indicated that the photodegradation rates follow first order kinetics. Under maximum loading of TiO2, with five catalyst slides having 20 bilayers of polyelectrolyte/TiO2 on each, 100 mL of 10 mg/L dye solution could be degraded completely in 4 h. The same slides could be reused with the same efficiency for several cycles. This study demonstrates that nanoparticles can be used in wastewater treatment using a simple immobilization technique. This makes the process an attractive option for scale up.

Polyelectrolyte microcapsules for sustained delivery of water-soluble drugs

Polyelectrolyte capsules composed of weak polyelectrolytes are introduced as a simple and efficient system for spontaneous encapsulation of low molecular weight water-soluble drugs. Polyelectrolyte capsules were prepared by layer-by-layer (LbL) assembling of weak polyelectrolytes, poly(allylamine hydrochloride) (PAH) and poly (methacrylic acid) (PMA) on polystyrene sulfonate (PSS) doped CaCO3 particles followed by core removal with ethylene-diaminetetraacetic add (EDTA). The loading process was observed by confocal laser scanning microscopy (CLSM) using tetramethylrhodamineisothiocyanate labeled dextran (TRITC-dextran) as a fluorescent probe. The intensity of fluorescent probe inside the capsule decreased with increase in cross-linking time. Ciprofloxacin hydrochloride (a model water-soluble drug) was spontaneously deposited into PAH/PMA capsules and their morphological changes were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The quantitative study of drug loading was also elucidated which showed that drug loading increased with initial drug concentration, but decreased with increase in pH. The loaded drug was released in a sustained manner for 6 h, which could be further extended by cross-linking the capsule wall. The released drug showed significant antibacterial activity against E. coli. These findings indicate that such capsules can be potential carriers for water-soluble drugs in sustained/controlled drug delivery applications. (C) 2010 Elsevier B.V. All rights reserved.